1. Field of the Invention
This invention relates in general to the construction of humidifiers and in particular to a new and useful respiratory air humidifier which includes foils of a material which is impermeable to water but permeable to steam or vapor formed as individual walls or a plurality of hollow tubules.
2. Reference to Copending Application
This invention is an improvement over an invention disclosed and described in U.S. Pat. No. 4,010,748.
This patent discloses a respiratory air humidifier which contains a water impermeable but vapor or steam permeable foil which is charged on one side while the gas to be humidified passes over the other side. The construction describes in detail an evaporation surface of star-shaped form which achieves a large evaporation output. The present invention is an improvement over such a construction inasmuch as it provides means for further reducing the size of the respiratory air humidifier without reducing the evaporation surface and thus the evaporation output.
3. Description of the Prior Art
The invention concerns respiratory air humidifiers for respirators with surface evaporation where the evaporation surface is formed by a water-impermeable, but vapor-permeable foil which is charged on one side with water, and where the gas to be humidified passes over the other side charged with gas.
Comfort in a technical sense is the condition of well being with regard to the climate of a room to a person using this room. It depends on the temperature, the velocity of the air, and not insubstantially on the vapor pressure. The relative humidity should not be too high, or humid, but not too low, or dry, either. If too dry the air passages will dry out.
Subdivided according to the principal design, the following respiratory air humidifiers are known:
Cascade humidifiers have a system in which the inhaling air is conducted through the heated water to humidify the air. Water droplets, which have been carried along, are retained over granules arranged above the water surface. A disadvantage of the cascade humidifiers is that the compressible volume varies with the amount of water fill. Beyond that, the apparatus is so large that it cannot be arranged in front of the patient's mouth for respiration. With long feed lines, the air cools off, however. This way a part of the moisture contained in the inhaling air is condensed. The condensate must be kept away from the patient by extra devices. (Cascade Humidifiers by Bennet, Santa Monica, California, 1971).
Wick-type humidifiers operate like the cascade humidifiers, also as surface humidifiers. But due to the wick, the air does not come in such close contact with the water. It passes over the moistened wicks, which absorb heated water from a storage vessel. These humidifiers have the same disadvantages as the cascade humidifiers. But since they can be made smaller, they can be arranged close to the patient. The problems of condensation are thus more favorable, but on the other hand, sufficient humidification of the respiratory air is not always secured.
Another humidifier uses hot steam injection into the inhaling air current. For generating the hot steam, a heated plate is arranged in the humidifier on which an adjustable amount of water is evaporated. The resulting steam arrives in the inhaling air system and humidifies the inhaling air. Humidifiers working on this principle can be made very small. Condensation is therefore not a problem. Difficult, however, is the adjustment of the proper amount of water for humidifying the respiratory air. With low breathing volumes, this may result in overheating, with a too large breathing volume, on the other hand, the air may not be sufficiently humidified and the temperature may be too low.
According to the invention the foil forms a wall of hollow fibers with an inside diameter of 300 microns, and is about 15 microns thick.
The decisive advantage of this construction lies substantially in the much larger evaporation surface, which can be accommodated with the same cross-section and the same length. The aspect ratio compared to the known star-shaped arrangement is 50:1. The respiratory air humidifier according to the invention can thus be made much smaller with the same evaporation output.
In one embodiment of the invention, the gas-carrying hollow fibers arranged parallel to each other in a housing as an assembly, as well as a perforated water feed pipe and a water discharge pipe, both arranged inside the assembly, are secured on the end faces in a sealing compound.
The water required for the evaporation is fed safely on the shortest way. By wetting the surfaces from hollow to hollow fiber, the necessary uniform admission with water is ensured. The desired humidification of the gas (in the present case the respiratory air) conducted through the interior of the hollow fibers is also corresponding safe. The easily dosable amount of water or the regulation of the amount of respiratory air flowing through the device ensures any desired humidity value in the respiratory air. The water which has not entered the hollow fibers is discharged in a simple manner through the water discharge pipe.
The design of the water feed pipe and of the water discharge pipe as a U-shaped pipe with the connections arranged side by side in the direction of the hollow fibers and secured in the sealing compound makes the technical production simple. In this embodiment only the connection to a water supply is required.
In a further development of the invention, which is of advantage for large amounts of respiratory air, the water-carrying hollow fibers are arranged on a plate, side by side in two layers arranged in a right angle to each other on both sides and secured over an air passage in a sealing compound. The water supply and discharge are effected by connecting spouts to an end bore in the sealing compound.
In addition to the advantage of a larger amount of respiratory air with a lower resistance to flow, this embodiment permits further simplification of the production. The hollow fibers are wound about the plate provided with the air passage crossed over in two layers. In this position they are cast on the four sides of the plate with the sealing compound which can be a filler. The hollow fibers are cut up through bores extending from opposite diagonal points toward both sides into the filler and are provided with free connections for the water supply and its discharge.
Accordingly it is an object of the invention to provide a respiratory air humidifier which comprises foil means of a material which is impermeable to water but permeable to steam and which includes means for directing water over one side of the foil means and means for directing breathing gas to be humidified over the other side of the foil means wherein the foil means comprises individual walls of a plurality of hollow tubules having inside diameters of less than about 300 microns and being of about 15 microns thick.
A further object of the invention is to provide a respiratory air humidifier which includes a conduit having an connection piece at one end with small size passages which communicate with the interiors of individual tubes made of material which is permeable to vapor and impermeable to water and which further includes centrally arranged enlarged water carrying conduit or pipe having a plurality of perforations or openings therein for the distribution of water over the individual tubules and a discharge pipe for carrying away the water which is circulated over the oustide surface of the tubules.
A further object of the invention is to provide a humidifier which is adapted to be disposed in a respiratory airstream which includes a plate having individual tubules stretched across the plate and longitudinal and transverse directions and which communicate through end bores or passages with water and which define a grid through which the air to be humidified is circulated.
A further object of the invention is to provide a humidifier which is simple in design, rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference should be had to the accompanying drawing and descriptive matter in which there are illustrated preferred embodiments of the invention.